The present invention generally relates to electrophotography and more particularly, to a developing apparatus for use in an image forming apparatus based on an electrophotographic copying process.
Commonly, in a developing method for visualizing an electrostatic latent image formed on an electrostatic latent image support member, by causing charged toner to electrostatically adhere onto said electrostatic latent image, quality of images to be formed differs according to particle sizes of the toner which is employed.
More specifically, upon comparison of an image formed by toner of large particle diameters with that formed by toner of small particle diameters, edge portions (contour) and fine lines are represented more clearly and definitely in the image formed by the toner with small particle diameters.
However, in the toner manufactured by the grinding or classification process, particle diameters of toner are generally in the Gaussian distribution, ranging from large particle diameters to small particle diameters in a wide range.
Meanwhile, there has been proposed a developing apparatus so arranged that, with a toner layer thickness restricting member held in contact under pressure with a toner support member which contacts toner in a toner hopper, the toner supported on the surface of the toner support member due to on rotation of said support member is applied to the developing apparatus while being restricted by said restricting member, for example, in Japanese Patent Laid-Open Publication Tokkaisho No. 62-267782 assigned to the same assignee as in the present invention. In the developing apparatus of this kind, however, there is such a problem that, since toner with smaller article diameters is more likely to be held on the toner support member, while toner with larger particle diameters will be scraped off the surface of the toner support member by the restricting member. This occurs when the developing is started, with toner being filled in the developing apparatus in the empty state. Although a fine grained image in a good quality may be obtained through preferential consumption of the toner with small particle diameters at an initial stage of the developing, the image tends to be coarse in grain as the larger particle diameter toner comes to be gradually consumed thereafter.